modify tmux and ssh to recover SSH_AUTH_SOCK after tmux reconnect

base/.ssh/rc

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+# Fix SSH auth socket location so agent forwarding works with tmux.
+if test "$SSH_AUTH_SOCK" ; then
+  ln -sf $SSH_AUTH_SOCK ~/.ssh/ssh_auth_sock
+fi
+